1. Field of the Invention
The present invention relates to a receiving apparatus, an information processing method and a program, and more particularly to a receiving apparatus which is adapted to speedily respond to that warning information has been transmitted thereto, an information processing method and a program.
2. Description of the Related Art
An Orthogonal Frequency Division Multiplexing (OFDM) system for modulating each of orthogonal carriers with Phase Shift Keying (PSK) or Quadrature Amplitude Modulation (QAM) by using a large number of orthogonal carriers has been proposed as a modulation system for territorial digital broadcastings.
The OFDM system has the feature that although since the entire transmission band is divided into segments by a large number of sub-carriers, a band per one sub-carrier wave becomes narrow and a transmission rate becomes slow, the total transmission rate is unchanged from that of the existing modulation system.
In addition, the OFDM system has the feature that since a large number of sub-carriers are transmitted in parallel with one another, a symbol speed becomes slow. For this reason, the OFDM system also has the feature that a time length of a multipath relative to a time length of one symbol can be shortened, whereby the OFDM system is hardly influenced by the multipath.
In addition, since data is allocated to a plurality of sub-carriers, the OFDM system has the feature that a transmitting circuit can be configured by using an Inverse Fast Fourier Transform (IFFT) arithmetically operating circuit for carrying out Inverse Fast Fourier Transform in a phase of modulation, and a receiving circuit can be configured by using a Fast Fourier Transform (FFT) arithmetically operating circuit for carrying out Fourier Transform in a phase of demodulation.
From the features described above, the OFDM system is applied to the terrestrial digital broadcasting on which an influence of a multipath interference is strongly exerted in many cases. The standard such as Integrated Services Digital Broadcasting-Terrestrial (ISDB-T), for example, is known as the standard for the terrestrial digital broadcasting adopting the OFDM system.
It is regulated in the ISDB-T standard that in order to transmit either additional information on transmission control for a modulated wave or earthquake motion warning information, an Auxiliary Channel (AC) signal with information of 204 bits as one unit is transferred by using a predetermined sub-carrier in an OFDM symbol. The AC signal is an additional information signal about the broadcasting.
The AC signal is subjected to differential BPSK modulation. The differential BPSK modulation system is a modulation system for differentially coding a data stream to be transmitted, and making information (0, 1) after completion of the differential coding a complex signal (I signal, Q signal) having signal points of (+4/3, 0), and (−4/3, 0).
FIG. 1 is a diagram showing a structure of a frame of the AC signal.
In FIG. 1, numerical value added to corresponding one of under portions of multiple pieces of information represents what number bit corresponding to one of the multiple pieces of information corresponds to with the head of the AC signal as a reference. A transverse length of each of the multiple pieces of information is not proportional to the number of bits.
As shown in an upper stage of FIG. 1, the AC signal with the information of 204 bits as one unit is composed of a reference signal of 1 bit for differential modulation, structure identification of 3 bits, and additional information of 200 bits on transmission control for a modulated wave or earthquake motion warning information in the order from the head.
The reference signal is a signal coming to have a reference amplitude and a reference phase for the differential demodulation.
The structure identification is a signal for identifying a structure of the AC signal. 000, 010, 011, 100, 101 or 111 of the structure identification represents that the additional information on the transmission control for the modulated wave is transmitted. Also, 001 or 110 of the structure identification represents that the earthquake motion warning information is transmitted. When the structure identification is either 001 or 110, the earthquake motion warning information is transmitted with the following 200 bits.
It is noted that the earthquake motion warning information is transmitted by using the AC carrier of a segment of No. 0. The entire frequency band used in the digital broadcasting complying with the ISDB-T standard is divided into 13 segments from No. 0 to No. 12. Also, the carrier (AC carrier) which is transmitted by using the AC signal is regulated every segment.
The earthquake motion warning information of 200 bits is composed of a synchronous signal of 13 bits, a start/end flag of 2 bits, an update flag of 2 bits, signal identification of 3 bits, earthquake motion warning detailed information of 88 bits, Cyclic Redundancy Check (CRC) of 10 bits, and parity bits of 82 bits.
The synchronous signal is information representing a head position of the earthquake motion warning information. Specifically, W0=“1010111101110” when the structure identification is 001, and W1=“0101000010001” as an inverted word of W0 when the structure identification is 110 are alternately inserted in frames.
The start/end flag is 00 “when the earthquake motion warning detailed information is present,” and is 11 “when the earthquake motion warning detailed information is absent.”
The update flag is increased one-by-one basis whenever a change is caused in the contents of a series of earthquake motion warning detailed information which is transmitted when the start/end flag is 00, and informs a receiver of that the signal identification or the earthquake motion information has been updated.
The signal identification is a signal which is used to identify a kind of earthquake motion warning detailed information following the signal identification.
000 of the signal identification represents that “an appropriate area of the earthquake motion warning detailed information is present,” and 001 of the signal identification represents that “an appropriate area of the earthquake motion warning detailed information is absent.” The wording “an appropriate area of the earthquake motion warning detailed information is present” means that an objective area of the earthquake motion warning detailed information is present in a broadcasting area. Also, the wording “an appropriate area of the earthquake motion warning detailed information is absent” means that the objective area of the earthquake motion warning detailed information is absent in the broadcasting area.
In addition, 010 of the signal identification represents that “a test signal of the earthquake motion warning detailed information is present in an appropriate area,” and 011 of the signal identification represents that “a test signal of the earthquake motion warning detailed information is absent in the appropriate area.” 111 represents “the earthquake motion warning detailed information is absent (identification of broadcasters).” Each of 100, 101 and 110 of the signal identification is undefined. When the signal identification is any one of 000, 001, 010, and 011, information of current time information which sends the earthquake motion warning information, information representing the objective area of the earthquake motion warning, and information on an earthquake center of the earthquake motion warning are transmitted as the earthquake motion warning detailed information.
In addition, when the signal identification is 111, the identification of the broadcasters is transmitted as the earthquake motion warning detailed information. Also, when the signal identification is any one of 100, 101 and 110, ALL1 is transmitted as the earthquake motion warning detailed information.
CRC is a CRC code which is generated in accordance with a generating polynomial with respect to bits from 22nd bit to 112nd bit with the head of the AC signal as a reference.
The parity bit is an error correction code which is generated from a shortened code (187, 107) of a difference set cycle code (273, 191) with respect to the bits from 18th bit to 122nd bit with the head of the AC signal as a reference.
The technique described above, for example, is disclosed in a non-patent document of STD-B31<http://www.arib.or.jp/english/html/overview/doc/2-STD-B31v1—8.pdf>.